Talk to the teacher first, then the supervisor of that teacher if there is still a problem. Always go to the teacher first, though, in a non-confrontational manner. When my son was in fifth grade, his English teacher gave the boys an assignment due after Succos, that could not in any way, shape, or form be done by the boys without EXTENSIVE help from Mom and Dad. In many cases, the parents DID the work, because it was taking so long for them to oversee their sons’ work AND prepare for the yomim tovim. My husband literally sat for hours with my son, explaining what the teacher was asking him to do, and starting him off, then watching him do the work. It was torture for ALL of us.
We had open school night with the teachers, and many, many of the parents verbally attacked this teacher. (I am not maskim to such a tactic, but I could not really blame them for expressing their anger in unison). The teacher simply misjudged the assignment’s level of difficulty vis a vis these students. She should have started out with them all working together in class, to better understand exactly what was expected of them. She also should have been more realistic about a) the truly enormous amount of work she had assigned and b) the fact that the parents would not want their kids to be doing written assignments during chol hamoed. In the end, the best thing to do is approach the teacher privately and reasonably, see what the expectations are, and explain why you believe it might not be doable. There is always a place to compromise.